D 11.9 An amplifier has an open-loop gain with a nominal value of 1000 but can vary from unit to unit by as much as ±50% of nominal. It is required to apply negative feedback to this amplifier so that the variability of the closed-loop gain of the resulting feedback amplifier is limited to ±1%. What is the largest possible nominal value of closed-loop gain that can be achieved? Now if three of these feedback amplifiers are placed in cascade, what is the nominal value of the gain of the resulting cascade amplifier? What is the expected variability of this gain?